1. Field of the Invention
This invention relates to a metal magnetic powder for magnetic recording media, and more particularly relates to a metal magnetic powder having an excellent stability, and a method of producing the same.
2. Description of the Prior Art
There is an increasing demand for high-density recording in the 8-mm video tape, DAT, magnetic disc or the like. Prerequisites for a magnetic recording medium suitable for high-density recording are that the saturation magnetization of the magnetic powder for the medium is as large as possible, and the coercive force of the powder is as high as possible, or the like. As a magnetic powder which satisfies these prerequisites, there is a metal magnetic powder which consists mainly of iron, and to which cobalt, nickel and the like are added. It is necessary to maintain the magnitude of the coercive force H.sub.c of the powder within such an extent that the magnetic head is not saturated. The coercive force of about 1600 Oe is satisfactory, and, in general, the coercive force is greater than 1300 1100 Oe, but not greater than 1600 Oe is desirable.
On the other hand, the magnetic recording medium functions better as the saturation magnetization of the magnetic powder is higher. Hence, high saturation magnetization is being required.
However, the metal powder is easily oxidized because it is very active. Hence, there is a problem that, although the metal powder has a high saturation magnetization immediately after its production, the saturation magnetization of the metal powder is largely decreased due to oxidation.
In order to improve such instability, there have been tried that oxide films are positively formed on the surfaces of particles of the metal powder, or other oxidation-preventing coatings are formed on the surfaces. These attempts have resulted in, however, insufficient stability, or insufficient magnitude of saturation magnetization.